German Patent Application DE 19847982 A1 describes a device for measuring vibrations of a rotor blade of a wind turbine generator system, which device is capable of ascertaining deformation of the rotor blade using a distance sensor as a linear element. Elements of the device are attached to a rotor wall by an adhesive joint. The above-mentioned patent application notes at the outset that adhesive joints require considerable mechanical skill and effort for retrofitting them on existing rotor blades.